Field of the Invention
The invention relates to devices and methods for removing tissue from body passageways, such as removal of atherosclerotic plaque from arteries, utilizing a rotational atherectomy device. In particular, the invention relates to improvements in a rotational atherectomy device having a biasing clutch and/or a shock absorbing element.
Description of the Related Art
Atherectomy is a non-surgical procedure to open blocked coronary arteries or vein grafts by using a device on the end of a catheter to cut or shave away atherosclerotic plaque (a deposit of fat and other substances that accumulate in the lining of the artery wall). For the purposes of this application, the term “abrading” is used to describe the grinding and/or scraping action of such an atherectomy head.
Atherectomy is performed to restore the flow of oxygen-rich blood to the heart, to relieve chest pain, and to prevent heart attacks. It may be done on patients with chest pain who have not responded to other medical therapy and on certain of those who are candidates for balloon angioplasty (a surgical procedure in which a balloon catheter is used to flatten plaque against an artery wall) or coronary artery bypass graft surgery. It is sometimes performed to remove plaque that has built up after a coronary artery bypass graft surgery.
Atherectomy uses a rotating shaver or other device placed on the distal end of a catheter to slice away or destroy plaque. At the beginning of the procedure, medications to control blood pressure, dilate the coronary arteries, and prevent blood clots are administered. The patient is awake but sedated. The catheter is inserted into an artery in the groin, leg, or arm, and threaded through the blood vessels into the blocked coronary artery. The cutting head is positioned against the plaque and activated, and the plaque is ground up or suctioned out.
The types of atherectomy are rotational, directional, and transluminal extraction. Rotational atherectomy uses a high speed rotating shaver to grind up plaque. Directional atherectomy was the first type approved, but is no longer commonly used; it scrapes plaque into an opening in one side of the catheter. Transluminal extraction coronary atherectomy uses a device that cuts plaque off vessel walls and vacuums it into a bottle. It is used to clear bypass grafts.
Performed in a cardiac catheterization lab, atherectomy is also called removal of plaque from the coronary arteries. It can be used instead of, or along with, balloon angioplasty.
Several devices have been disclosed that perform rotational atherectomy. For instance, U.S. Pat. No. 5,360,432, issued on Nov. 1, 1994 to Leonid Shturman, and titled “Abrasive drive shaft device for directional rotational atherectomy” discloses an abrasive drive shaft atherectomy device for removing stenotic tissue from an artery, and is incorporated by reference herein in its entirety. The device includes a rotational atherectomy apparatus having a flexible, elongated drive shaft having a central lumen and a segment, near its distal end, coated with an abrasive material to define an abrasive segment. At sufficiently high rotational speeds, the abrasive segment expands radially, and can sweep out an abrading diameter that is larger than its rest diameter. In this manner, the atherectomy device may remove a blockage that is larger than the catheter itself. Use of an expandable head is an improvement over atherectomy devices that use non-expandable heads; such non-expandable devices typically require removal of particular blockages in stages, with each stage using a differently-sized head.
U.S. Pat. No. 5,314,438 (Shturman) shows another atherectomy device having a rotatable drive shaft with a section of the drive shaft having an enlarged diameter, at least a segment of this enlarged diameter section being covered with an abrasive material to define an abrasive segment of the drive shaft. When rotated at high speeds, the abrasive segment is capable of removing stenotic tissue from an artery.
A typical atherectomy device includes a single-use disposable portion, which can be attached and detached from a non-disposable control unit (also referred to as a controller). The disposable portion includes elements that are exposed to saline and to the bodily fluids of the patient, such as a handle, a catheter, a rotatable drive shaft, and an abrasive head. The handle includes a turbine that rotates the drive shaft, and a knob that can longitudinally advance and retract the drive shaft along the catheter. Often, the device has a foot switch that activates the handle.
Typical known atherectomy devices use pneumatic power to drive the drive shaft, with the controller managing the amount of compressed air that is delivered to the turbine in the handle. The compressed air spins the turbine that, in turn, spins the drive shaft, and spins an abrasive crown attached to the drive shaft. Orbiting motion of the crown enlarges and widens the channel opening of a restricted or blocked vascular vessel.
There is currently a great deal of effort devoted to incorporating other types of rotational actuators into the atherectomy devices, primarily to replace the need for a source of compressed air. A motor requires a way limit the torque delivered to the drive shaft. For instance, if the distal end of the drive shaft encounters an obstacle and gets stuck (i.e., stops rotating), it is preferable that the torque delivered to the drive shaft be limited, so that the drive shaft does not wind up excessively and abruptly release. Such a sudden release of energy may result in damage to the patient or the device, and should be avoided.
Accordingly, there exists a need for a clutch between the motor and the drive shaft in a rotational atherectomy device.